U.S. patent application number 12/598002 was filed with the patent office on 2010-08-12 for systems and methods for making a middle distillate product and lower olefins from a hydrocarbon feedstock.
This patent application is currently assigned to SHELL OIL COMPANY. Invention is credited to David John Brosten, George A. Hadjigeorge, Weijian Mo, Rene Samson.
Application Number | 20100200460 12/598002 |
Document ID | / |
Family ID | 39496135 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100200460 |
Kind Code |
A1 |
Brosten; David John ; et
al. |
August 12, 2010 |
SYSTEMS AND METHODS FOR MAKING A MIDDLE DISTILLATE PRODUCT AND
LOWER OLEFINS FROM A HYDROCARBON FEEDSTOCK
Abstract
A system comprising a riser reactor for contacting a gas oil
feedstock with a catalytic cracking catalyst under catalytic
cracking conditions to yield a riser reactor product comprising a
cracked gas oil product and a spent cracking catalyst; a separator
for separating said riser reactor product into said cracked gas oil
product and said spent cracking catalyst; a regenerator for
regenerating said spent cracking catalyst to yield a regenerated
catalyst; a intermediate reactor for contacting a gasoline
feedstock with said regenerated catalyst under high severity
conditions to yield a cracked gasoline product and a used
regenerated catalyst; a first conduit connected to the intermediate
reactor and the riser reactor, the first conduit adapted to send
the used regenerated catalyst to the riser reactor to be used as
the catalytic cracking catalyst; and a second conduit connected to
the intermediate reactor and the regenerator, the second conduit
adapted to send the used regenerated catalyst to the regenerator to
yield a regenerated catalyst.
Inventors: |
Brosten; David John;
(Lindsey Court Anacortes, WA) ; Hadjigeorge; George
A.; (Sugar Land, TX) ; Mo; Weijian; (Sugar
Land, TX) ; Samson; Rene; (Amsterdam, NL) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Assignee: |
SHELL OIL COMPANY
Houston
TX
|
Family ID: |
39496135 |
Appl. No.: |
12/598002 |
Filed: |
April 28, 2008 |
PCT Filed: |
April 28, 2008 |
PCT NO: |
PCT/US2008/061734 |
371 Date: |
February 25, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60914961 |
Apr 30, 2007 |
|
|
|
Current U.S.
Class: |
208/59 ;
422/141 |
Current CPC
Class: |
C10G 2300/4093 20130101;
C10G 3/57 20130101; Y02P 30/20 20151101; C10G 2300/807 20130101;
C10G 2400/04 20130101; C10G 51/026 20130101; C10G 51/06 20130101;
C10G 2300/1059 20130101; C10G 2300/1048 20130101; C10G 3/47
20130101; C10G 51/00 20130101; C10G 3/62 20130101; C10G 3/49
20130101; C10G 2400/20 20130101; C10G 11/18 20130101 |
Class at
Publication: |
208/59 ;
422/141 |
International
Class: |
B01J 8/18 20060101
B01J008/18; C10G 51/00 20060101 C10G051/00 |
Claims
1. A system comprising: a riser reactor for contacting a gas oil
feedstock with a catalytic cracking catalyst under catalytic
cracking conditions to yield a riser reactor product comprising a
cracked gas oil product and a spent cracking catalyst; a separator
for separating said riser reactor product into said cracked gas oil
product and said spent cracking catalyst; a regenerator for
regenerating said spent cracking catalyst to yield a regenerated
catalyst; an intermediate reactor for contacting a gasoline
feedstock with said regenerated catalyst under high severity
conditions to yield a cracked gasoline product and a used
regenerated catalyst; a first conduit connected to the intermediate
reactor and the riser reactor, the first conduit adapted to send
the used regenerated catalyst to the riser reactor to be used as
the catalytic cracking catalyst; and a second conduit connected to
the intermediate reactor and the regenerator, the second conduit
adapted to send the used regenerated catalyst to the regenerator to
yield a regenerated catalyst.
2. The system of claim 1, further comprising a selector valve
connected to the first conduit and the second conduit, adapted to
divide the used regenerated catalyst between the first conduit and
the second conduit.
3. The system of claim 1, further comprising: a third conduit
connected to the regenerator and the intermediate reactor, the
third conduit adapted to send the regenerated catalyst to the
intermediate reactor; and a fourth conduit connected to the
regenerator and the riser reactor, the fourth conduit adapted to
send the regenerated catalyst to the riser reactor.
4. The system of claim 3, further comprising a second selector
valve connected to the third conduit and the fourth conduit,
adapted to divide the regenerated catalyst between the third
conduit and the fourth conduit.
5. The system of claim 1, further comprising a separation system
for separating the cracked gas oil product into at least two of a
cracked gas stream, a cracked gasoline stream, a cracked gas oil
stream, and a cycle oil stream.
6. The system of claim 5, further comprising a recycle conduit to
send the cycle oil stream to the riser reactor.
7. The system of claim 1, further comprising a second separation
system for separating the cracked gasoline product into at least
two of a ethylene stream, a propylene stream, a butylene stream,
and a cracked gasoline stream.
8. The system of claim 7, further comprising a second recycle
conduit to send the cracked gasoline stream to the intermediate
reactor.
9. The system of claim 1, wherein the intermediate reactor
comprises a fast fluidized bed reactor, a riser reactor, or a dense
bed reactor.
10. A method comprising: catalytically cracking a gas oil feedstock
within an FCC riser reactor zone by contacting under suitable
catalytic cracking conditions within said FCC riser reactor zone
said gas oil feedstock with a middle distillate selective cracking
catalyst to yield an FCC riser reactor product comprising a cracked
gas oil product and a spent cracking catalyst; regenerating said
spent cracking catalyst to yield a regenerated cracking catalyst;
contacting a gasoline feedstock with said regenerated cracking
catalyst within an intermediate cracking reactor operated under
suitable high severity cracking conditions so as to yield a cracked
gasoline product, comprising at least one lower olefin compound,
and a used regenerated cracking catalyst; separating said cracked
gasoline product into a lower olefin product, comprising said at
least one lower olefin compound; using at least a portion of said
used regenerated cracking catalyst as said middle distillate
selective catalyst; and regenerating at least a portion of said
used regenerated cracking catalyst to yield a regenerated cracking
catalyst.
11. The method of claim 10, wherein the middle distillate selective
cracking catalyst comprises amorphous silica alumina and a
zeolite.
12. The method of claim 10, further comprising: using said lower
olefin product as an olefin feed to a polyolefin manufacturing
system
13. The method of claim 10, wherein said intermediate cracking
reactor defines a intermediate reaction zone and a stripping zone,
wherein into said intermediate reaction zone is introduced said
gasoline feedstock and said regenerated cracking catalyst and from
said intermediate reaction zone is withdrawn said cracked gasoline
product, and wherein into said stripping zone is introduced steam
and from said stripping zone is withdrawn said used regenerated
cracking catalyst.
14. The method of claim 13, further comprising: introducing into
said intermediate reaction zone a ZSM-5 additive.
15. The method of claim 10, wherein said suitable catalytic
cracking conditions are such as to provide for a conversion of said
gas oil feedstock in the range of from 40 to 90 weight percent of
the total gas oil feedstock.
16. The method of claim 10, wherein said used regenerated cracking
catalyst includes a small concentration of carbon.
Description
FIELD OF THE INVENTION
[0001] The present disclosure relates to systems and methods for
making a middle distillate product and lower olefins from a
hydrocarbon feedstock.
BACKGROUND OF THE INVENTION
[0002] The fluidized catalytic cracking (FCC) of heavy hydrocarbons
to produce lower boiling hydrocarbon products such as gasoline is
well known in the art. FCC processes have been around since the
1940's. Typically, an FCC unit or process includes a riser reactor,
a catalyst separator and stripper, and a regenerator. A FCC
feedstock is introduced into the riser reactor wherein it is
contacted with hot FCC catalyst from the regenerator. The mixture
of the feedstock and FCC catalyst passes through the riser reactor
and into the catalyst separator wherein the cracked product is
separated from the FCC catalyst. The separated cracked product
passes from the catalyst separator to a downstream separation
system and the separated catalyst passes to the regenerator where
the coke deposited on the FCC catalyst during the cracking reaction
is burned off the catalyst to provide a regenerated catalyst. The
resulting regenerated catalyst is used as the aforementioned hot
FCC catalyst and is mixed with the FCC feedstock that is introduced
into the riser reactor.
[0003] Many FCC processes and systems are designed so as to provide
for a high conversion of the FCC feedstock to products having
boiling temperatures in the gasoline boiling range. There are
situations, however, when it is desirable to provide for the high
conversion of the FCC feedstock to middle distillate boiling range
products, as opposed to gasoline boiling range products, and to
lower olefins. However, making lower olefins requires high severity
and high reaction temperature reaction conditions. These conditions
normally result in low middle distillate product yield and poor
middle distillate product quality. It is therefore very difficult
in the conventional cracking of hydrocarbons to provide
simultaneously for both a high yield of lower olefins and a high
yield of middle distillate products.
[0004] United States Patent Application Publication 2006/0178546
discloses a process for making middle distillate and lower olefins.
The process includes catalytically cracking a gas oil feedstock
within a riser reactor zone by contacting under suitable catalytic
cracking conditions within the riser reactor zone the gas oil
feedstock with a middle distillate selective cracking catalyst that
comprises amorphous silica alumina and a zeolite to yield a cracked
gas oil product and a spent cracking catalyst. The spent cracking
catalyst is regenerated to yield a regenerated cracking catalyst.
Within an intermediate cracking reactor such as a dense bed reactor
zone and under suitable high severity cracking conditions a
gasoline feedstock is contacted with the regenerated cracking
catalyst to yield a cracked gasoline product and a used regenerated
cracking catalyst. The used regenerated cracking catalyst is
utilized as the middle distillate selective catalyst. United States
Patent Application Publication 2006/0178546 is herein incorporated
by reference in its entirety.
[0005] United States Patent Application Publication 2006/0178546
allows the use of a used regenerated cracking catalyst from an
intermediate cracking reactor to be used as a middle distillate
selective catalyst in a riser reactor zone.
[0006] There is a need in the art to use customized mixtures of
regenerated cracking catalyst and used regenerated cracking
catalyst in a riser reactor zone.
[0007] There is a further need in the art to regenerate the used
regenerated cracking catalyst from the intermediate cracking
reactor prior to using it in the riser reactor zone.
[0008] There is a further need in the art to regenerate the used
regenerated cracking catalyst from the intermediate cracking
reactor prior to using it in the riser reactor zone.
[0009] There is a further need in the art to simultaneously produce
middle distillate and lower olefin products from a hydrocarbon
feedstock.
[0010] There is a further need in the art to be able to
independently adjust process conditions, reactor severity, catalyst
temperature and/or catalyst activity of the intermediate cracking
reactor and the riser reactor zone.
SUMMARY OF THE INVENTION
[0011] In one aspect, the invention provides a system comprising a
riser reactor for contacting a gas oil feedstock with a catalytic
cracking catalyst under catalytic cracking conditions to yield a
riser reactor product comprising a cracked gas oil product and a
spent cracking catalyst; a separator for separating said riser
reactor product into said cracked gas oil product and said spent
cracking catalyst; a regenerator for regenerating said spent
cracking catalyst to yield a regenerated catalyst; a intermediate
reactor for contacting a gasoline feedstock with said regenerated
catalyst under high severity conditions to yield a cracked gasoline
product and a used regenerated catalyst; a first conduit connected
to the intermediate reactor and the riser reactor, the first
conduit adapted to send the used regenerated catalyst to the riser
reactor to be used as the catalytic cracking catalyst; and a second
conduit connected to the intermediate reactor and the regenerator,
the second conduit adapted to send the used regenerated catalyst to
the regenerator to yield a regenerated catalyst.
[0012] In another aspect, the invention provides a method
comprising catalytically cracking a gas oil feedstock within an FCC
riser reactor zone by contacting under suitable catalytic cracking
conditions within said FCC riser reactor zone said gas oil
feedstock with a middle distillate selective cracking catalyst to
yield an FCC riser reactor product comprising a cracked gas oil
product and a spent cracking catalyst; regenerating said spent
cracking catalyst to yield a regenerated cracking catalyst;
contacting a gasoline feedstock with said regenerated cracking
catalyst within an intermediate cracking reactor operated under
suitable high severity cracking conditions so as to yield a cracked
gasoline product, comprising at least one lower olefin compound,
and a used regenerated cracking catalyst; separating said cracked
gasoline product into a lower olefin product, comprising said at
least one lower olefin compound; using at least a portion of said
used regenerated cracking catalyst as said middle distillate
selective catalyst; and regenerating at least a portion of said
used regenerated cracking catalyst to yield a regenerated cracking
catalyst.
[0013] Advantages of the invention include one or more of the
following:
[0014] Improved systems and methods for enhanced conversion of a
hydrocarbon feedstock to middle distillate and lower olefin
products.
[0015] Improved systems and methods for using customized mixtures
of regenerated cracking catalyst and used regenerated cracking
catalyst in a riser reactor zone.
[0016] Improved systems and methods for regenerating the used
regenerated cracking catalyst from the intermediate cracking
reactor prior to using it in the riser reactor zone.
[0017] Improved systems and methods for simultaneously producing
middle distillate and lower olefin products from a hydrocarbon
feedstock.
[0018] Improved systems and methods for independently adjusting
process conditions, reactor severity, catalyst temperature and/or
catalyst activity of the intermediate cracking reactor and the
riser reactor zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a hydrocarbon feedstock conversion
system.
[0020] FIG. 2 illustrates an intermediate cracking reactor.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Referring now to FIG. 1, there is illustrated a process flow
schematic of system 10. Gas oil feedstock passes through conduit 12
and is introduced into the bottom of FCC riser reactor 14. FCC
riser reactor 14 defines an FCC riser reactor zone, or cracking
reaction zone, wherein the gas oil feedstock is mixed with a
catalytic cracking catalyst. Steam may also be introduced into the
bottom of FCC riser reactor 14 by way of conduit 15. This steam can
serve to atomize the gas oil feedstock or as a lifting fluid.
Typically, when steam is used to atomize the gas oil feedstock, the
amount of steam used can be in the range of from 1 to 5 or 10
weight percent of the gas oil feedstock. The catalytic cracking
catalyst can be a used regenerated cracking catalyst or a
regenerated cracking catalyst, or a combination of both
catalysts.
[0022] The used regenerated cracking catalyst is a regenerated
cracking catalyst that has been used in intermediate reactor 16 in
the high severity cracking of a gasoline feedstock. The used
regenerated cracking catalyst passes from intermediate reactor 16
and is introduced into FCC riser reactor 14 by way of conduit 18a.
Alternatively, used regenerated cracking catalyst may be sent to
regenerator 20 through conduit 18b. Selector valve 19 may be used
to determine how much used regenerated cracking catalyst is sent to
conduit 18a and how much is sent to conduit 18b.
[0023] Regenerated cracking catalyst may also be mixed with the gas
oil feedstock. The regenerated cracking catalyst passes from
regenerator 20 through conduit 22 and is introduced by way of
conduit 24 into FCC riser reactor 14 wherein it is mixed with the
gas oil feedstock.
[0024] Passing through FCC riser reactor 14 that is operated under
catalytic cracking conditions is a mixture of gas oil feedstock and
hot catalytic cracking catalyst that forms an FCC riser reactor
product comprising a mixture of a cracked gas oil product and a
spent cracking catalyst. The FCC riser reactor product passes from
FCC riser reactor 14 and is introduced into stripper system or
separator/stripper 26.
[0025] The separator/stripper 26 can be any conventional system
that defines a separation zone or stripping zone, or both, and
provides means for separating the cracked gas oil product and spent
cracking catalyst. The separated cracked gas oil product passes
from separator/stripper 26 by way of conduit 28 to separation
system 30. The separation system 30 can be any system known to
those skilled in the art for recovering and separating the cracked
gas oil product into the various FCC products, such as, for
example, cracked gas, cracked gasoline, cracked gas oils and cycle
oil. The separation system 30 may include such systems as absorbers
and strippers, fractionators, compressors and separators or any
combination of known systems for providing recovery and separation
of the products that make up the cracked gas oil product.
[0026] The separation system 30, thus, defines a separation zone
and provides means for separating the cracked gas oil product into
cracked products. The cracked gas, cracked gasoline and cracked gas
oils respectively pass from separation system 30 through conduits
32, 34, and 36. The cycle oil passes from separation system 30
through conduit 38 and is introduced into FCC riser reactor 14. The
separated spent cracking catalyst passes from separator/stripper 26
through conduit 40 and is introduced into regenerator 20.
Regenerator 20 defines a regeneration zone and provides means for
contacting the spent cracking catalyst with an oxygen-containing
gas, such as air, under carbon burning conditions to remove carbon
from the spent cracking catalyst. The oxygen-containing gas is
introduced into regenerator 20 through conduit 42 and the
combustion gases pass from regenerator 20 by way of conduit 44.
[0027] The regenerated cracking catalyst passes from regenerator 20
through conduit 22. The stream of regenerated cracking catalyst
passing through conduit 22 may be divided into two streams with at
least a portion of the regenerated catalyst passing from
regenerator 20 through conduit 22 passing through conduit 46 to the
intermediate reactor 16 and with the remaining portion of the
regenerated catalyst passing from regenerator 20 passing through
conduit 24 to FCC riser reactor 14. To assist in the control of the
cracking conditions in the FCC riser reactor 14, the split between
the at least a portion of regenerated cracking catalyst passing
through conduit 46 and the remaining portion of regenerated
cracking catalyst passing through conduit 24 can be adjusted as
required with selector valve 23.
[0028] Intermediate reactor 16 may define a dense bed fluidization
zone and provides means for contacting a gasoline feedstock with
the regenerated cracking catalyst contained within the intermediate
reactor 16. The fluidization zone may be operated under high
severity cracking conditions so as to preferentially crack the
gasoline feedstock to lower olefin compounds, such as ethylene,
propylene, and butylenes, and to yield a cracked gasoline product.
The cracked gasoline product passes from intermediate reactor 16
through conduit 48.
[0029] Alternatively, intermediate reactor 16 may be a fast
fluidized bed or riser reactor, as are known in the art.
[0030] The used regenerated cracking catalyst may pass from
intermediate reactor 16 through selector valve 19 and conduit 18a
and is introduced into FCC riser reactor 14, and/or used
regenerated cracking catalyst may pass from intermediate reactor 16
through selector valve 19 and conduit 18b and is introduced into
regenerator 20. The gasoline feedstock is introduced into the
intermediate reactor 16 through conduits 50 and/or 56 and steam may
be introduced into the intermediate reactor 16 by way of conduit
52. The gasoline feedstock and steam are introduced into the
intermediate reactor 16 so as to provide for a fluidized bed of the
regenerated catalyst. A ZSM-5 additive may be added to the
regenerated catalyst of the dense phase reactor 16 or introduced
into the intermediate reactor 16 through conduit 54.
[0031] A portion, or the entire amount, of the cracked gasoline
passing from separation system 30 through conduit 34 may be
recycled and introduced into the intermediate reactor 16 by way of
conduit 56. This recycling of the cracked gasoline product can
provide for an additional conversion across the overall process
system of the gas oil feedstock to lower olefins. The cracked
gasoline product of conduit 48 passes to olefin separation system
58. The olefin separation system 58 can be any system known to
those skilled in the art for recovering and separating the cracked
gasoline product into lower olefin product streams. The olefin
separation system 58 may include such systems as absorbers and
strippers, fractionators, compressors and separators or any
combination of known systems or equipment providing for the
recovery and separation of the lower olefin products from a cracked
gasoline product. Yielded from the separation system 58 may be an
ethylene product stream, propylene product stream, and butylenes
product stream each of which respectively pass from the olefin
separation system 58 though conduits 60, 62, and 64. Separation
system 58 may also yield a cracked gasoline stream 65, which may be
sent to recycle conduit 56. Not shown in FIG. 1 is the one or more
olefin manufacturing systems to which any of the lower olefin
products may be passed as a polymerization feedstock to be used in
the manufacture of a polyolefin.
[0032] With system 100, all of the used regenerated cracking
catalyst from intermediate reactor 16 may be sent to regenerator 20
through conduit 18b, so that FCC riser reactor 14 can be operated
with 100% regenerated cracking catalyst from regenerator 20 through
conduit 24. Alternatively, all of the used regenerated cracking
catalyst from intermediate reactor 16 may be sent to FCC riser
reactor 14 through conduit 18a, so that FCC riser reactor 14 can be
operated with up to 100% used regenerated cracking catalyst from
intermediate reactor 16 through conduit 18a. Alternatively, a
portion of the used regenerated cracking catalyst from intermediate
reactor 16 may be sent to regenerator 20 through conduit 18b and a
portion of the used regenerated cracking catalyst may be sent to
FCC riser reactor 14 through conduit 18a, so that FCC riser reactor
14 can be operated with a customized mixture of the regenerated
cracking catalyst and the used regenerated cracking catalyst, to
achieve the desired process conditions.
[0033] FIG. 2 illustrates in somewhat greater detail the
intermediate reactor 16. Intermediate reactor 16 is a vessel that
defines an intermediate reaction zone 66 and a stripping zone 68.
Regenerated catalyst is introduced into the intermediate reaction
zone 66 by way of conduit 46, gasoline feedstock is introduced into
the intermediate reaction zone 66 by way of conduits 50 and/or 56,
and ZSM-5 additive is introduced into the intermediate reaction
zone 66 by way of conduit 54. Steam is introduced into the
stripping zone 68 by way of conduit 52 and used regenerated
cracking catalyst is withdrawn from the stripping zone 68 by way of
conduits 18a and/or 18b.
[0034] The systems and methods of the invention provide for the
processing of a heavy hydrocarbon feedstock to selectively produce
middle distillate boiling range products and lower olefins. It has
been discovered that the use of an intermediate cracking reactor,
which can include reactors of the type such as a dense phase
reactor, or fixed fluidized bed reactor, or a riser reactor,
between the catalyst regenerator and an FCC riser reactor of a
conventional FCC process or unit can provide for an improved middle
distillate yield and for enhanced selectivity toward the production
of lower olefins.
[0035] The invention may utilize the intermediate cracking reactor
to provide for the cracking of a gasoline feedstock that preferably
boils in the gasoline temperature range to yield lower olefins and
for the conditioning of the catalyst so that when it is used in the
cracking of the FCC feedstock in the FCC riser reactor the reactor
conditions are more suitable for the production of a middle
distillate product.
[0036] An additional feature of the invention is that it can
further include a system integrated into the process to provide for
the processing of the lower olefins yielded from the intermediate
cracking reactor. This olefin processing system can perform such
functions as the separation of the lower olefins into specific
olefin product streams, such as an ethylene product stream, a
propylene product stream or a butylenes product stream or any
combination thereof, and the use of the lower olefins as a
polymerization feed in the manufacture of polyolefins.
[0037] A gas oil feedstock may be introduced into the bottom of an
FCC riser reactor where it is mixed with hot cracking catalyst such
as a regenerated cracking catalyst or a used regenerated cracking
catalyst or a combination of both catalysts. The starting catalytic
cracking catalyst used and regenerated to ultimately become the
regenerated cracking catalyst can be any suitable cracking catalyst
known in the art to have cracking activity at the elevated
temperatures contemplated by the invention.
[0038] Preferred catalytic cracking catalysts include fluidizable
cracking catalysts comprised of a molecular sieve having cracking
activity dispersed in a porous, inorganic refractory oxide matrix
or binder. The term "molecular sieve" as used herein refers to any
material capable of separating atoms or molecules based on their
respective dimensions. Molecular sieves suitable for use as a
component of the cracking catalyst include pillared clays,
delaminated clays, and crystalline aluminosilicates. Normally, it
is preferred to use a cracking catalyst that contains a crystalline
aluminosilicate. Examples of such aluminosilicates include Y
zeolites, ultrastable Y zeolites, X zeolites, zeolite beta, zeolite
L, offretite, mordenite, faujasite, and zeolite omega. Suitable
crystalline aluminosilicates for use in the cracking catalyst are X
and Y zeolites, for example Y zeolites.
[0039] U.S. Pat. No. 3,130,007, the disclosure of which is hereby
incorporated by reference in its entirety, describes Y-type
zeolites having an overall silica-to-alumina mole ratio between
about 3.0 and about 6.0, with a typical Y zeolite having an overall
silica-to-alumina mole ratio of about 5.0. It is also known that
Y-type zeolites can be produced, normally by dealumination, having
an overall silica-to-alumina mole ratio above about 6.0.
[0040] The stability and/or acidity of a zeolite used as a
component of the cracking catalyst may be increased by exchanging
the zeolite with hydrogen ions, ammonium ions, polyvalent metal
cations, such as rare earth-containing cations, magnesium cations
or calcium cations, or a combination of hydrogen ions, ammonium
ions and polyvalent metal cations, thereby lowering the sodium
content until it is less than about 0.8 weight percent, preferably
less than about 0.5 weight percent and or less than about 0.3
weight percent, calculated as Na.sub.2O. Methods of carrying out
the ion exchange are known in the art.
[0041] The zeolite or other molecular sieve component of the
cracking catalyst is combined with a porous, inorganic refractory
oxide matrix or binder to form a finished catalyst prior to use.
The refractory oxide component in the finished catalyst may be
silica-alumina, silica, alumina, natural or synthetic clays,
pillared or delaminated clays, mixtures of one or more of these
components and the like. The inorganic refractory oxide matrix may
comprise a mixture of silica-alumina and a clay such as kaolin,
hectorite, sepiolite and attapulgite. A finished catalyst may
contain between about 5 weight percent to about 40 weight percent
zeolite or other molecular sieve and greater than about 20 weight
percent inorganic, refractory oxide. In general, the finished
catalyst may contain between about 10 to about 35 weight percent
zeolite or other molecular sieve, between about 10 to about 30
weight percent inorganic, refractory oxide, and between about 30 to
about 70 weight percent clay.
[0042] The crystalline aluminosilicate or other molecular sieve
component of the cracking catalyst may be combined with the porous,
inorganic refractory oxide component or a precursor thereof by any
suitable technique known in the art including mixing, mulling,
blending or homogenization. Examples of precursors that may be used
include alumina, alumina sols, silica sols, zirconia, alumina
hydrogels, polyoxycations of aluminum and zirconium, and peptized
alumina. In one suitable method of preparing the cracking catalyst,
the zeolite is combined with an alumino-silicate gel or sol or
other inorganic, refractory oxide component, and the resultant
mixture is spray dried to produce finished catalyst particles
normally ranging in diameter between about 40 and about 80 microns.
If desired, however, the zeolite or other molecular sieve may be
mulled or otherwise mixed with the refractory oxide component or
precursor thereof, extruded and then ground into the desired
particle size range. Normally, the finished catalyst will have an
average bulk density between about 0.30 and about 0.90 gram per
cubic centimeter and a pore volume between about 0.10 and about
0.90 cubic centimeter per gram.
[0043] When the process is operated in the middle distillate
selective mode (or diesel mode) of operation, a middle distillate
selective cracking catalyst may be used. A middle distillate
selective cracking catalyst is similar to the above-described
preferred cracking catalyst in that it comprises a molecular sieve
dispersed in a porous, inorganic refractory oxide binder, but it
has some significant differences over the typical cracking
catalyst, which such differences are hereafter described in more
detail. The middle distillate cracking catalyst may exhibit
catalytic properties that provide for the selective cracking of a
gas oil feedstock to yield a cracked gas oil product that
preferentially includes middle distillate boiling range products
such as those in the diesel boiling range, such as from 230.degree.
C. to 350.degree. C.
[0044] The middle distillate selective cracking catalyst may
comprise zeolite or other molecular sieve component, an alumina
component and an additional porous, inorganic refractory matrix or
binder component. The middle distillate selective cracking catalyst
can be prepared by any method known to those skilled in the art
that provide for a catalytic cracking catalyst having the desired
composition. More specifically, the middle distillate selective
cracking catalyst can comprise alumina in the amount in the range
of from 40 wt. % to 65 wt. %, for example from 45 wt. % to 62 wt.
%, or from 50 wt. % to 58 wt. %, with the weight percent being
based on the total weight of the middle distillate selective
cracking catalyst, a porous inorganic refractory oxide matrix
component providing a matrix surface area, and a zeolite or other
molecular sieve component providing a zeolitic surface area. The
alumina component of the middle distillate selective cracking
catalyst can be any suitable type of alumina and from any suitable
source. Examples of suitable types of aluminas are those as
disclosed in U.S. Pat. No. 5,547,564 and U.S. Pat. No. 5,168,086,
which are herein incorporated by reference in their entirety, and
include, for example, alpha alumina, gamma alumina, theta alumina,
eta alumina, bayerite, pseudoboehmite and gibbsite.
[0045] The matrix surface area within the middle distillate
selective cracking catalyst that is provided by the porous
inorganic refractory oxide matrix component may be in the range of
from 20 to 90 square meters per gram of middle distillate selective
cracking catalyst. The zeolitic surface area within the middle
distillate selective cracking catalyst that is provided by the
zeolite or other molecular sieve component may be less than 140
square meters per gram.
[0046] In order for the middle distillate selective cracking
catalyst to have the desired catalytic property of preferentially
providing for the yield of middle distillate such as diesel, the
portion of the surface area of the middle distillate selective
cracking catalyst that is contributed by the zeolite or other
molecular sieve component, i.e. the zeolitic surface area, may be
less than 130 square meters per gram, for example less than 110
square meters per gram, or, less than 100 square meters per gram.
The zeolite or other molecular sieve component of the middle
distillate selective cracking catalyst are those aluminosilicates
selected from the group consisting of Y zeolites, ultrastable Y
zeolites, X zeolites, zeolite beta, zeolite L, offretite,
mordenite, faujasite, and zeolite omega.
[0047] The zeolitic surface area within the middle distillate
selective cracking catalyst may be as low as 20 square meters per
gram, but, generally, the lower limit is greater than 40 square
meters per gram. The lower limit for the zeolitic surface area
within the middle distillate selective cracking catalyst may exceed
60 square meters per gram, or, the zeolitic surface area may exceed
80 square meters per gram. Thus, for example, the portion of the
surface area of the middle distillate selective cracking catalyst
contributed by the zeolite or other molecular sieve component, i.e.
the zeolitic surface area, can be in the range of from 20 square
meters per gram to 140 square meters per gram, or in the range of
from 40 square meters per gram to 130 square meters per gram.
[0048] The ratio of the zeolitic surface area to the matrix surface
area within the middle distillate cracking catalyst is a property
thereof which is important in providing for a catalyst having the
desired cracking properties. The ratio of zeolitic surface area to
matrix surface area, thus, may be in the range of from 1:1 to 2:1,
for example, from 1.1:1 to 1.9:1, or, from 1.2:1 to 1.7:1.
Considering these ratios, the portion of the surface area of the
middle distillate selective cracking catalyst contributed by the
porous inorganic refractory oxide matrix component, i.e., the
matrix surface area, is generally in the range of from 20 square
meters per gram to 80 square meters per gram. One suitable range
for the matrix surface area is from 40 square meters per gram to 75
square meters per gram, or, the range is from 60 square meters per
gram to 70 square meters per gram.
[0049] In the case of the use of an FCC riser reactor that is
vertically arranged, lift gas or lift steam may also be introduced
into the bottom of the FCC riser reactor along with the gas oil
feedstock and the hot cracking catalyst. The regenerated cracking
catalyst that is yielded from the catalyst regenerator has a higher
temperature than the used regenerated cracking catalyst that is
yielded from the intermediate cracking reactor. Also, the used
regenerated cracking catalyst has deposited thereon as a result of
its use in the intermediate cracking reactor a certain amount of
coke. A particular catalyst or combination of catalysts may be used
to help control the conditions within the FCC riser reactor to
provide for certain desired cracking conditions required to provide
a desired product or mix of products.
[0050] The mixture of gas oil feedstock and hot cracking catalyst,
and, optionally, lift gas or steam, passes through the FCC riser
reactor wherein cracking takes place. The FCC riser reactor defines
a catalytic cracking zone and provides means for providing a
contacting time to allow the cracking reactions to occur. The
average residence time of the hydrocarbons in the FCC riser reactor
generally can be in the range of upwardly to about 5 to 10 seconds,
but usually is in the range of from 0.1 to 5 seconds. The weight
ratio of catalyst to hydrocarbon feed (catalyst/oil ratio)
generally can be in the range of from about 2 to about 100 and even
as high as 150. More typically, the catalyst-to-oil ratio can be in
the range of from 5 to 100. When steam is introduced into the FCC
riser reactor with the gas oil feedstock, the steam-to-oil weight
ratio can be in the range of from 0.01 to 5, and, more, typically,
it is in the range of from 0.05 to 1.5.
[0051] The temperature in the FCC riser reactor generally can be in
the range of from about 400.degree. C. to about 600.degree. C. More
typically, the FCC riser reactor temperature can be in the range of
from 450.degree. C. to 550.degree. C. The FCC riser reactor
temperatures may tend to be lower than those of typical
conventional fluidized catalytic cracking processes; because, the
inventive process is to provide for a high yield of middle
distillates as opposed to the production of gasoline as is often
sought with conventional fluidized catalytic cracking processes.
The control of certain of the process conditions within the FCC
riser reactor may be controlled by adjusting the ratio of
regenerated cracking catalyst from the catalyst regenerator to used
regenerated cracking catalyst from the intermediate cracking
reactor that is introduced into the bottom of the FCC riser
reactor.
[0052] The mixture of hydrocarbons and catalyst from the FCC riser
reactor pass as an FCC riser reactor product comprising cracked gas
oil product and spent cracking catalyst to a stripper system that
provides means for separating hydrocarbons from catalyst and
defines a stripper separation zone wherein the cracked gas oil
product is separated from the spent cracking catalyst. The stripper
system can be any system or means known to those skilled in the art
for separating FCC catalyst from a hydrocarbon product. In a
typical stripper operation, the FCC riser reactor product, which is
a mixture of cracked gas oil product and spent cracking catalyst
passes to the stripper system that includes cyclones for separating
the spent cracking catalyst from the vaporous cracked gas oil
product. The separated spent cracking catalyst enters the stripper
vessel from the cyclones where it is contacted with steam to
further remove cracked gas oil product from the spent cracking
catalyst. The coke content on the separated spent cracking catalyst
is, generally, in the range of from about 0.5 to about 5 weight
percent (wt. %), based on the total weight of the catalyst and the
carbon. Typically, the coke content on the separated spent cracking
catalyst is in the range of from or about 0.5 wt. % to or about 1.5
wt. %.
[0053] The separated spent cracking catalyst is then passed to a
catalyst regenerator that provides means for regenerating the
separated spent cracking catalyst and defines a regeneration zone
into which the separated spent cracking catalyst is introduced and
wherein carbon that is deposited on the separated spent cracking
catalyst is burned in order to remove the carbon to provide a
regenerated cracking catalyst having a reduced carbon content. The
catalyst regenerator typically is a vertical cylindrical vessel
that defines the regeneration zone and wherein the spent cracking
catalyst is maintained as a fluidized bed by the upward passage of
an oxygen-containing regeneration gas, such as air.
[0054] The temperature within the regeneration zone is, in general,
maintained in the range of from about 621.degree. C. to 760.degree.
C., and more, typically, in the range of from 677.degree. C. to
715.degree. C. The pressure within the regeneration zone typically
is in the range of from about atmospheric to about 345 kPa, for
example from about 34 to 345 kPa. The residence time of the
separated spent cracking catalyst within the regeneration zone is
in the range of from about 1 to about 6 minutes, and, typically,
from about 2 to about 4 minutes. The coke content on the
regenerated cracking catalyst is less than the coke content on the
separated spent cracking catalyst and, generally, is less than 0.5
wt. %, with the weight percent being based on the weight of the
regenerated cracking catalyst excluding the weight of the coke
content. The coke content of the regenerated cracking catalyst
will, thus, generally, be in the range of from about 0.01 wt. % to
or about 0.5 wt. %, for example the coke concentration on the
regenerated cracking catalyst may be less than 0.3 wt. %, or less
than 0.1 wt. %.
[0055] The regenerated cracking catalyst from the catalyst
regenerator is passed to the intermediate cracking reactor, which
can be as noted above a dense phase reactor, or a fixed fluidized
bed reactor, or a riser reactor, that provides means for contacting
a gasoline feedstock with the regenerated cracking catalyst and
which defines a reaction or cracking zone wherein the gasoline
feedstock is contacted with the regenerated cracking catalyst under
suitable high severity cracking conditions, either with or without
the presence of steam.
[0056] The type of intermediate cracking reactor may be a dense
phase reactor, a fast fluidized bed reactor, or a riser reactor.
The dense phase reactor can be a vessel that defines two zones,
including an intermediate reaction or cracking or dense phase
reaction zone, and a stripping zone. Contained within the
intermediate reaction zone of the vessel is regenerated cracking
catalyst that is fluidized by the introduction of the gasoline
feedstock and, optionally, steam, which is introduced into the
stripping zone.
[0057] One suitable dense phase reactor design includes a dense
phase reactor vessel that defines the intermediate reaction zone
and the stripping zone that are in fluid communication with each
other with the stripping zone located below the intermediate
reaction zone. To provide for a high steam velocity within the
stripping zone, as compared to its velocity within the intermediate
reaction zone, the cross sectional area of the stripping zone may
be less than the cross sectional area of the intermediate reaction
zone. The ratio of the stripping zone cross sectional area to the
intermediate reaction zone cross sectional area can be in the range
of from 0.1:1 to 0.9:1, for example from 0.2:1 to 0.8:1, or, from
0.3:1 to 0.7:1.
[0058] The geometry of the dense phase reactor vessel may be such
that it is generally cylindrical in shape. The length-to-diameter
ratio of the stripping zone is such as to provide for the desired
high steam velocity within the stripping zone and to provide enough
contact time within the stripping zone for the desired stripping of
the used regenerated catalyst that is to be removed from the dense
phase reactor vessel. Thus, the length-to-diameter dimension of the
stripping zone can be in the range of from 1:1 to 25:1, for
example, from 2:1 to 15:1, or, from 3:1 to 10:1.
[0059] The dense phase reactor vessel may be equipped with a
catalyst introduction conduit that provides regenerated catalyst
introduction means for introducing the regenerated cracking
catalyst from the catalyst regenerator into the intermediate
reaction zone of the dense phase reactor vessel. The dense phase
reactor vessel is further equipped with a used regenerated catalyst
withdrawal conduit that provides used regenerated catalyst
withdrawal means for withdrawing used regenerated catalyst from the
stripping zone of the dense phase reactor vessel. The gasoline
feedstock is introduced into the intermediate reaction zone by way
of a feed introduction conduit providing means for introducing a
gasoline feedstock into the intermediate zone of the dense phase
reactor, and the steam is introduced into the stripping zone by way
of a steam introduction conduit providing means for introducing
steam into the stripping zone of the dense phase reactor. The
cracked gasoline product is withdrawn from the intermediate
reaction zone by way of a product withdrawal conduit providing
means for withdrawing a cracked gasoline product from the
intermediate zone of the dense phase reactor.
[0060] The intermediate cracking reactor can be operated or
controlled independently from the operation or control of the FCC
riser reactor. This independent operation or control of the
intermediate cracking reactor provides the benefit of an improved
overall, i.e., across the entire process system including the FCC
riser reactor as well as the intermediate cracking reactor,
conversion of the gas oil feedstock into the desired end-products
of middle distillate and the lower olefins of ethylene, propylene
and butylenes. With the independent operation of the intermediate
cracking reactor, the severity of the FCC riser reactor cracking
conditions can be reduced to thereby provide for a higher yield of
middle distillate or other desired products in the gas oil reactor
product, and the severity of the intermediate cracking reactor can
be controlled to optimize the yield of lower olefins or other
desired products.
[0061] One way of controlling the operation of the intermediate
cracking reactor is by the introduction of steam along with the
gasoline feedstock into the intermediate cracking reactor. Thus,
the dense phase reaction zone is operated under such reaction
conditions as to provide for a cracked gasoline product and, for
example, to provide for a high cracking yield of lower olefins. The
high severity cracking conditions can include a temperature within
the dense phase or intermediate reaction zone that is in the range
from about 482.degree. C. to about 871.degree. C., for example, the
temperature is in the range of from 510.degree. C. to 871.degree.
C., or, from 538.degree. C. to 732.degree. C. The pressure within
the intermediate reaction zone can be in the range of from about
atmospheric to about 345 kPa, for example, from about 34 to 345
kPa.
[0062] Steam may be introduced into the stripping zone of the
intermediate cracking reactor and to be contacted with the
regenerated cracking catalyst contained therein and in the
intermediate reaction zone. The use of steam in this manner
provides, for a given gas oil conversion across the system, an
increase in the propylene yield and butylene yield. It has
generally been understood by those skilled in the art that in
conventional gas oil reactor cracking processes low severity gas
oil reactor cracking conditions result in less lower olefins yield
relative to high severity gas oil reactor cracking conditions. The
use of steam in the intermediate cracking reactor may provide
further enhancements in the yield of lower olefins therefrom.
[0063] The use of the steam is particularly desirable; because, for
a given gas oil conversion across the process system, and in the
cracking of the gasoline feedstock in the intermediate cracking
reactor, it can provide for an improved selectivity toward lower
olefin yield with an increase in propylene and butylenes yield.
Thus, when steam is used, the weight ratio of steam to gasoline
feedstock introduced into the intermediate cracking reactor, with
gasoline being introduced into the reaction zone and steam being
introduced into the stripping zone, can be in the range of upwardly
to or about 15:1, for example, the range may be from 0.1:1 to 10:1,
or, the weight ratio of steam to gasoline feedstock may be in the
range of from 0.2:1 to 9:1, or, from 0.5:1 to 8:1.
[0064] Used regenerated cracking catalyst is removed from the
intermediate cracking reactor and utilized as hot cracking catalyst
mixed with the gas oil feedstock that is introduced into the FCC
riser reactor and/or sent to the regenerator to be regenerated. One
aspect of using the used regenerated cracking catalyst in the FCC
riser reactor is that it provides for the partial deactivation of
the regenerated catalyst prior to its use as hot cracking catalyst
in the FCC riser reactor. What is meant by partial deactivation is
that the used regenerated cracking catalyst will contain a slightly
higher concentration of carbon than the concentration of carbon
that is on the regenerated cracking catalyst. This partial
deactivation of the regenerated cracking catalyst may provide for a
preferred product yield when the gas oil feedstock is cracked
within the riser reactor zone. The coke concentration on the used
regenerated cracking catalyst is greater than the coke
concentration on the regenerated cracking catalyst, but it is less
than that of the separated spent cracking catalyst. The coke
content of the used regenerated catalyst can be greater than 0.1
wt. % and even greater than 0.5 wt. %. For example, the coke
content of the used regenerated catalyst may be in the range of
from about 0.1 wt. % to about 1 wt. %, or from 0.1 wt. % to 0.6 wt.
%.
[0065] Another benefit provided by the use of the intermediate
cracking reactor is associated with the used regenerated cracking
catalyst having a temperature that is lower than the temperature of
the regenerated cracking catalyst. This lower temperature of the
used regenerated cracking catalyst in combination with the partial
deactivation, as discussed above, may provide further benefits in a
preferential product yield from the cracking of the gas oil
feedstock.
[0066] To assist in providing for the control of the process
conditions within the FCC riser reactor and to provide for a
desired product mix, the regenerated cracking catalyst can be
divided into at least a portion that is passed to the intermediate
cracking reactor and a remaining portion of the regenerated
cracking catalyst that is mixed with the gas oil feedstock to be
introduced into the FCC riser reactor. The at least a portion of
the regenerated cracking catalyst introduced into the intermediate
cracking reactor can be in the range of upwardly to 100 percent (%)
of the regenerated cracking catalyst yielded from the catalyst
regenerator depending upon the requirements of the process and the
desired product yields. Specifically, however, the at least a
portion of regenerated cracking catalyst will represent from about
10% to 100% of the separated regenerated catalyst withdrawn from
the catalyst regenerator. Also, the at least a portion of
regenerated cracking catalyst can be from about 30% to about 90%,
or from 50% to 95% of the separated regenerated catalyst that is
withdrawn from the catalyst regenerator.
[0067] In controlling the reaction conditions within the FCC riser
reactor, as already noted, a combination or mixture of used
regenerated cracking catalyst from the intermediate cracking
reactor and the regenerated cracking catalyst from the catalyst
regenerator is introduced into the FCC riser reactor with the gas
oil feedstock. The relative amount of the used regenerated cracking
catalyst to the regenerated cracking catalyst is adjusted so as to
provide for the desired gas oil cracking conditions within the FCC
riser reactor zone; but, generally, the weight ratio of the used
regenerated cracking catalyst to the regenerated cracking catalyst
is in the range of from 0.1:1 to 100:1, for example, from 0.5:1 to
20:1, or, from 1:1 to 10:1. For a system operated at steady state,
the weight ratio of used regenerated cracking
catalyst-to-regenerated cracking catalyst approximates the weight
ratio of the at least a portion of regenerated cracking catalyst
passing to the intermediate cracking reactor to the remaining
portion of regenerated cracking catalyst that is mixed with the gas
oil feedstock introduced into the FCC riser reactor, and, thus, the
aforementioned ranges are also applicable to such weight ratio.
[0068] It is notable that it is not a desired aspect of the
inventive process to introduce spent cracking catalyst into the
intermediate cracking reactor for a variety of reasons. For
instance, the spent cracking catalyst has much higher carbon
content than the regenerated cracking catalyst and, thus, its
activity does not favor the yielding of the more desirable lower
olefins. The regenerated cracking catalyst introduced into the
intermediate cracking reactor to be more than 50 weight percent of
the sum weight of the regenerated cracking catalyst and spent
cracking catalyst that is introduced into the intermediated
cracking reactor. The amount of spent cracking catalyst introduced
into the intermediate cracking reactor may be minimized and may be
less than 20 weight percent of the sum weight of the regenerated
cracking catalyst and spent cracking catalyst that is introduced
into the intermediate cracking reactor, for example, less than 10
weight percent, or, less than 5 weight percent.
[0069] Another method by which the process conditions within the
FCC riser reactor may be controlled and a desired product mix is
provided is through the addition of a ZSM-5 additive into the
intermediate cracking reactor, as opposed to its addition into the
FCC riser reactor. The ZSM-5 additive may be introduced into the
intermediate cracking reactor, in particular, when a dense phase
reactor is used, into the dense phase reaction zone thereof, along
or concurrently with the regenerated catalyst that is a middle
distillate selective cracking catalyst. When a ZSM-5 additive is
used along with the middle distillate selective cracking catalyst
in the intermediate cracking reactor, an improvement in the yield
of the lower olefins such as propylene and butylenes can be
achieved. Thus, it is desirable to introduce into the intermediate
cracking reactor, particularly when the regenerated catalyst that
is being introduced therein is a middle distillate selective
cracking catalyst, ZSM-5 additive in an amount upwardly to 30
weight percent, for example upwardly to 20 weight percent, or
upwardly to 18 weight percent, of the regenerated catalyst being
introduced into the intermediate cracking reactor. Thus, when ZSM-5
additive is introduced into the intermediate cracking reactor, the
amount may be in the range of from 1 to 30 weight percent of the
regenerated cracking catalyst being introduced into the
intermediate cracking reactor, for example from 3 to 20 weight
percent, or, from 5 to 18 weight percent.
[0070] The ZSM-5 additive is a molecular sieve additive selected
from the family of medium pore size crystalline aluminosilicates or
zeolites. Molecular sieves that can be used as the ZSM-5 additive
include medium pore zeolites as described in "Atlas of Zeolite
Structure Types," Eds. W. H. Meier and D. H. Olson,
Butterworth-Heineman, Third Edition, 1992, which is hereby
incorporated by reference in its entirety. The medium pore size
zeolites generally have a pore size from about 0.5 nm, to about 0.7
nm and include, for example, MFI, MFS, MEL, MTW, EUO, MTT, HEU,
FER, and TON structure type zeolites (IUPAC Commission of Zeolite
Nomenclature). Non-limiting examples of such medium pore size
zeolites, include ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35,
ZSM-38, ZSM-48, ZSM-50, silicalite, and silicalite 2. One suitable
zeolite is ZSM-5, which is described in U.S. Pat. Nos. 3,702,886
and 3,770,614, which are herein incorporated by reference in their
entirety.
[0071] ZSM-11 is described in U.S. Pat. No. 3,709,979; ZSM-12 in
U.S. Pat. No. 3,832,449; ZSM-21 and ZSM-38 in U.S. Pat. No.
3,948,758; ZSM-23 in U.S. Pat. No. 4,076,842; and ZSM-35 in U.S.
Pat. No. 4,016,245. Other suitable molecular sieves include the
silicoaluminophosphates (SAPO), such as SAPO-4 and SAPO-11 which is
described in U.S. Pat. No. 4,440,871; chromosilicates; gallium
silicates, iron silicates; aluminum phosphates (ALPO), such as
ALPO-11 described in U.S. Pat. No. 4,310,440; titanium
aluminosilicates (TASO), such as TASO-45 described in EP-A No.
229,295; boron silicates, described in U.S. Pat. No. 4,254,297;
titanium aluminophosphates (TAPO), such as TAPO-11 described in
U.S. Pat. No. 4,500,651; and iron aluminosilicates. All of the
above patents are incorporated herein by reference in their
entirety.
[0072] The ZSM-5 additive may be held together with a catalytically
inactive inorganic oxide matrix component, in accordance with
conventional methods.
[0073] U.S. Pat. No. 4,368,114 describes in detail the class of
zeolites that can be suitable ZSM-5 additives, and such patent is
incorporated herein by reference.
[0074] The combination of one or more of the above described
process variables and operating conditions allows for the control
of the conversion of the gas oil feedstock. Generally, it is
desired for the gas oil feedstock conversion to be in the range of
from 30 to 90 weight percent, for example, from 40 to 90 weight
percent. What is meant by gas oil feedstock conversion is the
weight amount of hydrocarbons contained in the gas oil feedstock
that has a boiling temperature greater than 221.degree. C. that is
converted in the FCC riser reactor to hydrocarbons having a boiling
temperature less than 221.degree. C. divided by the weight amount
of hydrocarbons contained in the gas oil feedstock having a boiling
temperature greater than 221.degree. C. As earlier noted, the
process may be operated so as to provide for the preferential or
selective yielding of middle distillate boiling range products and
lower olefins.
[0075] The feedstock charged to the process may be any heavy
hydrocarbon feedstock that may be or is typically charged to a
fluidized catalytic cracking unit that boil in the boiling range of
from 200.degree. C. to 800.degree. C., including, for example, gas
oils, resid, or other hydrocarbons. In general terms, hydrocarbon
mixtures boiling in the range of from 345.degree. C. to 760.degree.
C. can make particularly suitable feedstocks. Examples of the types
of refinery feed streams that can make suitable gas oil feedstocks
include vacuum gas oils, coker gas oil, straight-run residues,
thermally cracked oils and other hydrocarbon streams.
[0076] The gasoline feedstock charged to the dense phase reaction
zone may be any suitable hydrocarbon feedstock having a boiling
temperature that is in the gasoline boiling temperature range.
Generally, the gasoline feedstock comprises hydrocarbons boiling in
the temperature range of from about 32.degree. C. to about
204.degree. C. Examples of refinery streams that may be used as the
gasoline feedstock of the inventive process include straight run
gasoline, naphtha, catalytically cracked gasoline, and coker
naphtha.
[0077] The process may include the integration of the intermediate
cracking reactor with a system for separating the cracked gasoline
product into at least one lower olefin product, or a system for
manufacturing a polyolefin, or a combination of both such systems.
It is the enhanced production of lower olefins provided by the
process that makes it beneficial to integrate the FCC riser reactor
and intermediate cracking reactor of the system with the further
processing of the cracked gasoline product. Specifically, the
increased yield of lower olefins through the use of steam and/or
ZSM-5 additive in the intermediate cracking reactor provides the
incentive to integrate the aforementioned process steps. Thus, the
cracked gasoline product, comprising at least one lower olefin
compound, such as, ethylene, propylene, or butylene, may further be
passed to a separation system for separating the cracked gasoline
product into a lower olefin product comprising at least one lower
olefin compound. The lower olefin product may further be used as a
feedstock to a polyolefin manufacturing system whereby the lower
olefin is polymerized under suitable polymerization conditions
preferably in the presence of any suitable polymerization catalyst
known to those skilled in the art.
Illustrative Embodiments
[0078] In one embodiment of the invention, there is disclosed a
system comprising a riser reactor for contacting a gas oil
feedstock with a catalytic cracking catalyst under catalytic
cracking conditions to yield a riser reactor product comprising a
cracked gas oil product and a spent cracking catalyst; a separator
for separating said riser reactor product into said cracked gas oil
product and said spent cracking catalyst; a regenerator for
regenerating said spent cracking catalyst to yield a regenerated
catalyst; a intermediate reactor for contacting a gasoline
feedstock with said regenerated catalyst under high severity
conditions to yield a cracked gasoline product and a used
regenerated catalyst; a first conduit connected to the intermediate
reactor and the riser reactor, the first conduit adapted to send
the used regenerated catalyst to the riser reactor to be used as
the catalytic cracking catalyst; and a second conduit connected to
the intermediate reactor and the regenerator, the second conduit
adapted to send the used regenerated catalyst to the regenerator to
yield a regenerated catalyst. In some embodiments, the system also
includes a selector valve connected to the first conduit and the
second conduit, adapted to divide the used regenerated catalyst
between the first conduit and the second conduit. In some
embodiments, the system also includes a third conduit connected to
the regenerator and the intermediate reactor, the third conduit
adapted to send the regenerated catalyst to the intermediate
reactor; and a fourth conduit connected to the regenerator and the
riser reactor, the fourth conduit adapted to send the regenerated
catalyst to the riser reactor. In some embodiments, the system also
includes a second selector valve connected to the third conduit and
the fourth conduit, adapted to divide the regenerated catalyst
between the third conduit and the fourth conduit. In some
embodiments, the system also includes a separation system for
separating the cracked gas oil product into at least two of a
cracked gas stream, a cracked gasoline stream, a cracked gas oil
stream, and a cycle oil stream. In some embodiments, the system
also includes a recycle conduit to send the cycle oil stream to the
riser reactor. In some embodiments, the system also includes a
second separation system for separating the cracked gasoline
product into at least two of a ethylene stream, a propylene stream,
a butylene stream, and a cracked gasoline stream. In some
embodiments, the system also includes a second recycle conduit to
send the cracked gasoline stream to the intermediate reactor.
[0079] In one embodiment of the invention, there is disclosed a
method comprising catalytically cracking a gas oil feedstock within
an FCC riser reactor zone by contacting under suitable catalytic
cracking conditions within said FCC riser reactor zone said gas oil
feedstock with a middle distillate selective cracking catalyst to
yield an FCC riser reactor product comprising a cracked gas oil
product and a spent cracking catalyst; regenerating said spent
cracking catalyst to yield a regenerated cracking catalyst;
contacting a gasoline feedstock with said regenerated cracking
catalyst within an intermediate cracking reactor operated under
suitable high severity cracking conditions so as to yield a cracked
gasoline product, comprising at least one lower olefin compound,
and a used regenerated cracking catalyst; separating said cracked
gasoline product into a lower olefin product, comprising said at
least one lower olefin compound; using at least a portion of said
used regenerated cracking catalyst as said middle distillate
selective catalyst; and regenerating at least a portion of said
used regenerated cracking catalyst to yield a regenerated cracking
catalyst. In some embodiments, the middle distillate selective
cracking catalyst comprises amorphous silica alumina and a zeolite.
In some embodiments, the method also includes using said lower
olefin product as an olefin feed to a polyolefin manufacturing
system. In some embodiments, said intermediate cracking reactor
defines a intermediate reaction zone and a stripping zone, wherein
into said intermediate reaction zone is introduced said gasoline
feedstock and said regenerated cracking catalyst and from said
intermediate reaction zone is withdrawn said cracked gasoline
product, and wherein into said stripping zone is introduced steam
and from said stripping zone is withdrawn said used regenerated
cracking catalyst. In some embodiments, the method also includes
introducing into said intermediate reaction zone a ZSM-5 additive.
In some embodiments, said suitable catalytic cracking conditions
are such as to provide for a conversion of said gas oil feedstock
in the range of from 40 to 90 weight percent of the total gas oil
feedstock. In some embodiments, said used regenerated cracking
catalyst includes a small concentration of carbon.
[0080] Those of skill in the art will appreciate that many
modifications and variations are possible in terms of the disclosed
embodiments of the invention, configurations, materials and methods
without departing from their spirit and scope. Accordingly, the
scope of the claims appended hereafter and their functional
equivalents should not be limited by particular embodiments
described and illustrated herein, as these are merely exemplary in
nature.
* * * * *